A conventional rear suspension system for bicycles is specifically designed to reduce the shocks transferred to the riders during uneven roads. The rear suspension system is deformed to absorb the shocks from the roads so that the riders have comfortable riding experienced.
The conventional rear suspension system generally includes a shock absorbing member, chain stays, seat stays and multiple link units, the rear suspension system is activated to generate relative movement between the seat tube and the rear wheel so as to reduce the shocks transferred to the riders.
The conventional rear suspension system is connected with the chain unit which generally includes a chain ring which is connected to the bottom bracket axle and a sprocket unit which is connected to the rear wheel, a chain is driven between the chain ring and one of the sprockets.
The distance between the chain ring and the sprocket decides the tension of the chain which is supposed to have a proper tension so as to transfer the force from the chain ring to the sprocket and the rear wheel. If the tension is less than required, the chain might be dropped. All the pivotable points between the bottom bracket axle and the sprocket unit affect the distance mentioned above.
One of the conventional rear suspension system 80 known to applicant is shown in FIG. 8, and generally includes a frame 81, a seat tube 811, a down tube 812, a bottom bracket 813 connected to the conjunction of the seat tube 811 and the down tube 812 and chain stays 82 which are connected between the seat tube 811 and two dropouts 821. A swing unit 83 is pivotably connected to the seat tube 811 and seat stays 84 are connected between the two dropouts 821 and the swing unit 83. A shock absorbing member 85 is located within an area enclosed by the frame 81 and has one end pivotably connected to the frame 81 and the other end is pivotably connected to the swing unit 83.
Another conventional rear suspension system 90 known to applicant is shown in FIG. 9, and generally includes a frame 91, a seat tube 911, a down tube 912, a bottom bracket 913 connected to the conjunction of the seat tube 911 and the down tube 912 and chain stays 92 which are connected between the seat tube 911 and two dropouts 921. A swing unit 93 is pivotably connected to the seat tube 911 and seat stays 94 are connected between the two dropouts 921 and the swing unit 93. A shock absorbing member 95 is located within an area enclosed by the frame 91 and has one end pivotably connected to the frame 91 and the other end is pivotably connected to the swing unit 93.
The difference between the two conventional rear suspension systems is that the dropouts 821 and the chain stays 82 of the first conventional rear suspension system is integral to each other and the seat stays 84 are located above the dropouts 821. There is only one pivotal position P1 is located between the distance “L” between the bottom bracket 813 and the dropouts 8211. When the rear wheel is moved upward and the chain stays 82 pivot about the pivotal position P1. The movement of the chain stays 82 changes the distance from “L” to “L′” which is not equal to “L”. The change affects the tension of the chain.
The dropouts 921 and the chain stays 92 for the second conventional rear suspension system are pivotably connected to each other and the seat stays 94 are located beneath the dropouts 921. There are two pivotal positions “P2” and “P3”, the “P2” is located at the dropouts 921 and the chain stays 92, and the “P3” is located at the chain stays 92 and the seat tube 911. When the rear wheel is moved upward, both of the two pivotal positions P2 and P3 affect the distance from “L” to “L′”. The change is larger than that in the first conventional rear suspension system.
The present invention intends to provide a rear suspension system for bicycles and the distance between the bottom bracket and the rear wheel axle is maintained to be not changed so that the tension of the chain can be kept.